JPH06240333A - Reduced pressure-vacuum degassing method for molten steel or molten alloy - Google Patents

Abstract

PURPOSE:To efficiently and profitably execute degassing in a short time by dipping a refractive cylindrical slag partition tube at the upper part of a molten steel or a molten alloy in a ladle and evacuating it while blowing inert gas into the molten steel or the molten alloy in the ladle. CONSTITUTION:The ladle 2 incorporating the molten steel 1 is arranged into a vacuum vessel 3 and a cover 4 is air-tightly closed. Successively, the inner part of the vacuum vessel 3 is evacuated to execute the degassing refining to the molten steel 1. Then, at the upper part of the molten steel 1 in the ladle, the cylindrical slag partition tube 5 composed of the refractory is dipped. Further, the inert gas is blown from a lance 6 for gas blowing and/or a gas blowing plug or nozzle 7 at the bottom part or a deep layer part. As for this gas, Ar or Ar and oxygen are used. By this gas blowing, molten slag at the upper part of the molten steel 1 is rejected to the outside of the slag partition tube 5 to prevent the intrusion of the slag to an inside. By this method, the contact area between the free surface of the molten steel and gas phase is sufficiently secured and the degassing speed is improved and the molten steel of dead soft carbon, extra low nitrogen and extra low hydrogen is efficiently produced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to carbon [C], nitrogen [N], hydrogen [H] contained in molten steel or molten alloy.
The present invention relates to an efficient degassing method for removing nitrogen under reduced pressure and vacuum.

[0002]

2. Description of the Related Art Carbon, nitrogen or hydrogen contained in steels and alloys is required to be in a very small amount in order to improve workability, prevent aging and improve ductility and further improve low temperature toughness.

Generally, in the steel industry, degassing treatment of molten steel or molten alloy (hereinafter simply referred to as molten steel) is performed.
For example, it is carried out by using various decompression / vacuum refining equipment as shown on pages 671 to 685 of the third edition of Iron and Steel Handbook II, Ironmaking and Steelmaking. Regarding the degassing method (RH degassing method) using a molten steel circulation type depressurization / vacuum tank, a method of blowing gas into the molten steel in the depressurization / vacuum tank (hereinafter, simply referred to as a vacuum tank) is described in, for example, Japanese Patent Laid-Open No. Hei 2 It is publicly known from JP-A-217412 or JP-A-3-61316, and a certain effect can be expected in improving the degassing rate. However, such a method has a small amount of molten steel in the vacuum tank, and therefore the molten steel depth is extremely shallow, and the injected gas is released from the molten steel without sufficiently participating in the reaction, increasing the amount of injected gas. However, the blown gas is blown out from the molten steel and splashes the molten steel, increasing the splash and making stable degassing impossible. On the other hand, the VOD method described on page 711 of the Ironmaking Steelmaking Edition, 3rd Edition Iron and Steel Manual II can secure the gas injection depth into the molten steel, but the slag existing on the molten steel surface of the ladle or inevitably generated is free of molten steel. The surface area is covered and the contact area between the molten steel, which is the degassing reaction site, and the gas phase is extremely reduced, and the degassing efficiency is extremely poor.

[0004]

2. Description of the Related Art There is an urgent need to provide a degassing method for efficiently and promptly removing carbon, nitrogen or hydrogen contained in molten steel to an extremely low concentration.

[0005]

DISCLOSURE OF THE INVENTION The present invention reduces the pressure of molten steel
It is an object of the present invention to provide a degassing method for carrying out vacuum treatment to produce ultra-low carbon, ultra-low nitrogen and ultra-low hydrogen molten steel efficiently and economically in a short time.

[0006]

DISCLOSURE OF THE INVENTION The present invention is to solve the problems of the prior art in an advantageous manner, in which a ladle containing molten steel or molten alloy is installed inside a vacuum chamber, In carrying out degassing refining of molten steel or molten alloy of, the cylindrical slag partition tube made of refractory is immersed in the upper part of the molten steel in the ladle, and the molten steel in the ladle is evacuated while injecting an inert gas. The present invention relates to a method for degassing molten steel or molten alloy. The present invention will be described below with reference to the drawings.

[0007]

1 is a drawing showing a typical example of a method for carrying out the method of the present invention. FIG. 1 (a) is an overall view showing an embodiment of the method of the present invention, and FIG. 1 (b) is a principle when discharging the inner slag of the cylindrical slag partition tube of the method of the present invention to the outside. It is a figure.

Molten steel or molten alloy to be degassed 1
The ladle 2 accommodating the above is installed in the vacuum tank 3, the cylindrical slag partition tube 5 is immersed in the molten steel or the molten alloy 1 from the upper part of the ladle 2, and the vacuum tank lid 4 is attached to the vacuum tank via the sealing mechanism 8. 3, while simultaneously evacuating the vacuum chamber, gas injection lance 6 and / or gas injection plug or nozzle 7 at the same time.
Gas injection is carried out via.

The degassing reaction proceeds at the interface (gas / liquid interface) between the liquid phase of molten steel and the gas phase of gas. At this time, the rate of each degassing reaction is represented by the equations (1 ′) to (3 ′),
In order to increase the degassing rate, it is necessary to increase the value of the reaction rate constant k _X. Since k _X is proportional to the reaction area, therefore, the gas / liquid interface area must be increased in order to increase the degassing reaction rate and rapidly produce molten steel containing ultra-low carbon, ultra-low nitrogen and ultra-low hydrogen. There is a need for a method of doing so and specific means for doing so.

[0010]

[Equation 1]

The free surface of molten steel, which occupies an important part of the reaction site, is generally covered with molten slag. In such a case, it is impossible to remove the molten slag from the molten free surface only by blowing gas, and it is not possible to sufficiently secure the degassing reaction site.

The root of the technical idea of the present invention is to secure a free surface of molten steel, which is the main reaction site, by immersing a cylindrical dipping pipe in molten steel from the upper part of the ladle, and blowing it into the upper part of molten steel by gas injection. By removing certain molten slag outside the cylindrical dip tube and preventing it from entering the inside of the cylindrical dip tube, the degassing rate can be increased by ensuring a sufficient contact area between the molten steel free surface and the vapor phase. There is a point to increase.

Further, in the formulas (1) to (3), the CO, H ₂ and N ₂ bubbles generated inside the molten steel have a large required pressure for bubble generation when the slag thickness existing on the molten steel free surface is large. The degassing rate decreases in proportion to the slag thickness. Therefore, elimination of slag from the molten steel free surface is extremely important for improving the degassing rate.

It is preferable to ensure that the inner diameter of the cylindrical dip tube is 50% or more of the inner diameter of the ladle, and the difference between the outer diameter of the cylindrical dip tube and the inner diameter of the ladle is discharged from the inside of the cylindrical dip tube. It is preferable to secure about 10 cm for retaining the accumulated slag. Further, the immersion depth may be shallow,
Basically, 5 to prevent backflow of the removed slag.
At least cm should be secured.

In the method of the present invention, the molten steel is fluidized,
Gas injection is essential to provide the driving force to remove the slag on the molten steel free surface from within the cylindrical dip tube.
The molten steel flow can be freely controlled by changing the flow rate and the injection depth of the injection gas.

In addition, gas-blowing increases the gas-liquid reaction interface area, which is the contact area between the blowing bubbles and the molten steel,
The degassing rate increases.

When denitrifying and decarburizing molten steel by applying the method of the present invention, in order to maintain or increase the oxygen concentration of the molten steel, oxygen gas or oxygen-containing gas is blown directly into the molten steel. It may be blown through the nozzle 7 or may be blown onto the surface of the molten steel using the blow lance 6.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 250 tons of molten steel was decarburized in a degassing furnace as shown in FIG. The slag thickness in the ladle is 55-150 mm
Is. The inner diameter of the ladle is 3.5 m, the inner diameter of the cylindrical dipping tube is 2.0 m, and the dipping depth is 20 cm. The distance between the inner wall of the ladle and the cylindrical dipping tube is 25 cm. The flow rate of Ar gas blown from the plug is 200 to 400 (Nl / mi
n), lance blowing Ar flow rate is 800 to 2500 (Nl
/ Min), and Ar blowing was carried out while evacuating. At this time, when the oxygen concentration [O] of the molten steel before decarburization was 0.025 mass% or less, oxygen gas was mixed with the lance blown Ar and blown into the molten steel.

FIG. 2 shows the change with time of the [C] concentration. Compared with the conventional method, in the method of the present invention, it is possible to decarburize to an extremely low carbon concentration in a short time, and it is possible to produce an extremely low carbon molten steel.

Example 2 250 tons of killed molten steel was dehydrogenated in a degassing furnace as shown in FIG.

The slag thickness in the ladle is 50 to 70 mm. Inner diameter of ladle is 3.5m, inner diameter of cylindrical dip tube is 2.5
m, and the immersion depth is 20 cm. The distance between the inner wall of the ladle and the cylindrical dipping tube is 25 cm. The Ar gas blowing flow rate from the plug was 400 (Nl / min) and the lance blowing Ar flow rate was 1500 to 2000 (Nl / min), and Ar blowing was performed while vacuum exhausting.

FIG. 3 shows the relationship between the hydrogen concentration [H] ₀ before degassing and the hydrogen concentration [H] _end after degassing for 20 minutes. Compared with the conventional method, the method of the present invention was capable of dehydrogenating to an extremely low concentration and was able to produce an extremely low hydrogen molten steel.

Example 3 A 250 ton molten steel was denitrified in a degassing furnace as shown in FIG. The slag thickness in the ladle is 70 mm.
The inner diameter of the ladle is 3.5 m, the inner diameter of the cylindrical dip tube is 2.5 m, the dipping depth is 20 cm, and the distance between the inner wall of the ladle and the cylindrical dip tube is 25 cm. The Ar gas blowing flow rate from the plug was 300 to 600 (Nl / min) and the lance blowing Ar flow rate was 1500 to 2000 (Nl / min), and Ar blowing was performed while vacuum exhausting.

FIG. 4 shows the nitrogen concentrations [N] ₀ and 2 before degassing.
The relationship with the nitrogen concentration [N] _end after 0 min degassing is shown. Compared with the conventional method, in the method of the present invention, denitrification was possible to an extremely low concentration in a short time, and an extreme nitrogen molten steel could be melted.

[0026]

EFFECTS OF THE INVENTION The degassing rate of molten steel is increased, and molten steel having ultra-low carbon, ultra-low nitrogen and ultra-low hydrogen concentration can be produced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example and a principle of a degassing facility for carrying out the present invention.

FIG. 2 is a drawing showing changes with time of [C] concentration.

FIG. 3 is a diagram showing a relationship of [H] concentration before and after degassing treatment.

FIG. 4 is a drawing showing a relationship of [N] concentration before and after degassing treatment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Molten steel or molten alloy 2 ... Ladle 3 ... Vacuum tank 4 ... Vacuum tank lid 5 ... Cylindrical immersion pipe 6 ... Gas injection lance 7 ... Gas injection plug or nozzle 8 ... Seal mechanism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Muneyasu Nasu 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Steel Works

Claims (3)

[Claims] 1. When a ladle containing molten steel or molten alloy is installed inside a vacuum chamber to perform degassing refining of molten steel or molten alloy in the ladle, a refractory material is formed on the molten steel in the ladle. A depressurization / vacuum degassing method for molten steel or molten alloy in which a cylindrical slag partition tube is dipped and the molten steel in the ladle is evacuated while injecting an inert gas. 2. The method according to claim 1, wherein Ar or Ar is introduced through a plurality of gas injection nozzles or gas injection plugs installed at the bottom or deep portion of the ladle.
A method for decompressing and vacuum degassing molten steel or molten alloy, which comprises blowing oxygen gas with oxygen. 3. The method according to claim 1, wherein a lance having a gas blowing nozzle is immersed in the molten steel in the ladle to carry out gas blowing, and at the same time, the bottom or the deep layer of the ladle. Depressurization of molten steel or molten alloy characterized by blowing Ar or Ar and oxygen gas through a plurality of gas blowing nozzles or gas blowing plugs installed in
Vacuum degassing method.